Granulocyte-colony–stimulating factor (G-CSF) signaling in spinal microglia drives visceral sensitization following colitis

Abstract

Pain is a main symptom of inflammatory diseases and often persists beyond clinical remission. Although we have a good understanding of the mechanisms of sensitization at the periphery during inflammation, little is known about the mediators that drive central sensitization. Recent reports have identified hematopoietic colony-stimulating factors as important regulators of tumor- and nerve injury-associated pain. Using a mouse model of colitis, we identify the proinflammatory cytokine granulocyte-colony-stimulating factor (G-CSF or Csf-3) as a key mediator of visceral sensitization. We report that G-CSF is specifically up-regulated in the thoracolumbar spinal cord of colitis-affected mice. Our results show that resident spinal microglia express the G-CSF receptor and that G-CSF signaling mediates microglial activation following colitis. Furthermore, healthy mice subjected to intrathecal injection of G-CSF exhibit pronounced visceral hypersensitivity, an effect that is abolished by microglial depletion. Mechanistically, we demonstrate that G-CSF injection increases Cathepsin S activity in spinal cord tissues. When cocultured with microglia BV-2 cells exposed to G-CSF, dorsal root ganglion (DRG) nociceptors become hyperexcitable. Blocking CX3CR1 or nitric oxide production during G-CSF treatment reduces excitability and G-CSF-induced visceral pain in vivo. Finally, administration of G-CSF-neutralizing antibody can prevent the establishment of persistent visceral pain postcolitis. Overall, our work uncovers a DRG neuron-microglia interaction that responds to G-CSF by engaging Cathepsin S-CX3CR1-inducible NOS signaling. This interaction represents a central step in visceral sensitization following colonic inflammation, thereby identifying spinal G-CSF as a target for treating chronic abdominal pain.

Enteric Glia Modulate Macrophage Phenotype and Visceral Sensitivity following Inflammation

“…Glial cells modulate pain sensations at multiple points along the gut-brain axis, and some of the mechanisms we describe here for enteric glia are shared among these other populations of glia. For example, spinal microglia are activated by M-CSF and G-CSF and enhance painful stimuli ( Basso et al, 2017 ; Guan et al, 2016 ). It is unlikely that these mechanisms contribute to reduced visceral hypersensitivity in our study since serum levels of these chemokines were not significantly affected by either inflammation or deletion of glial Cx43.…”

Chronic linaclotide treatment reduces colitis-induced neuroplasticity and reverses persistent bladder dysfunction

“…Therefore, colitis-induced enhancement of activation of spinal cord circuits could alter the spinal cord processing of bladder afferent input and therefore the sensory input then relayed into central micturition control regions. Such colitis-evoked changes could occur via the activation of spinal microglia, which are driving forces for maintaining pathological pain and for visceral and somatic sensitization following peripheral inflammation (34,35). Activated microglia release neuroexcitatory substances, proinflammatory cytokines, and growth factors, potentiating ectopic activation of dorsal horn neurons and neurite sprouting.…”

Endogenous control of inflammatory visceral pain by T cell‐derived opioids in IL‐10‐deficient mice

“…Cells were distributed as non-proliferative cells (M1), intermediately (M2), and highly proliferative (M3) cells. 33,35,36 Here, we examined the endogenous control of visceral hypersensitivity in a model of colitis in mice with impaired IL10-dependent immune regulation in which CD4 + T lymphocytes produce less PENK mRNA upon activation ( Figure 5). The activation status was also estimated by the up-regulation of CD69 and CD25 on CD4-gated cells (A, B, C, right panels).…”

“…34 The absence of T cell-mediated analgesia in TNBS-induced colitis may be related to central sensitization of spinal dorsal horn neurons and/or the significant loss of extrinsic afferent innervation in the mucosal layer. 33,35,36 Here, we examined the endogenous control of visceral hypersensitivity in a model of colitis in mice with impaired IL10-dependent immune regulation in which CD4 + T lymphocytes produce less PENK mRNA upon activation ( Figure 5). In this model where the number of macrophages is 3-4 times higher than that of CD4 + T lymphocytes, we show that the opioid-mediated analgesia, mostly due to CD4 + T lymphocytes, still operates.…”